Telephone system



Dec. 27, 1938. c. E. I OMAx TELEPHONE SYSTEM Filed Nov. 18, 1955 Patented Dec. 27, 1938 TELEPHONE SYSTEM Clarence E. Lomax, Oak Park, Ill., assigner to Associated Electric Laboratories, I nc., Chicago,

Ill., a corporation of Delaware Application November 18, 1935, Serial No. 50,25

10 Claims.

This invention relates in general to telephone systems and more particularly to a switching arrangement under control of a subscriber for amplifying received speech currents.

In accordance with the present invention an amplifier is provided at vthe main exchange individual to the subscribers line and the subscribers substation is provided with a switch for controlling switching. means at the exchange fory 3' cutting in and cutting out the amplifier.

Heretofore, in case a certain subscriber desired to have the received speech currents amplied, an amplifier and a switching arrangement was provided at the substation set and by means of a 3 key the subscriber switched the amplifier in and out of the circuit at will. The installation of the amplifying arrangement at the lsubstation has many disadvantages in that it requires a special wiring arrangement and apparatus which the average repair man cannot maintain and properly adjust.

It is more advantageous to install the amplifier at the main exchange because it is more economical, can be readily adjusted by a skilled person,

and is less apt to be tampered with or stolen.

The object of the invention is to place kan amplifier at the main exchange for amplifying 'speech currents transmitted toa subscribers line and to provide means at the subscribers sub- 0, station for cutting in and cutting out the amplif'ler atwill.

A feature of the invention relates to the circuit arrangement for enabling the subscriber to control the inclusion or exclusion of the amplifier in l5 the circuit over only the two line conductors com necting the substation to the main exchange.

A further feature relates to the subscriber con-Y trolled means for reducing the current to the transmitter so the signals in the receiver can be L0 amplified without causing howling between' th transmitter and receiver. y f

Another feature relates Vto the means at the substation for grounding one of the line conductors to place the remote amplifier in or ,out of the circuit in combination with the circuit arrangements whereby the connection of this ground is ineffective until a loop circuit is closed over the two vline conductors ofthe subscribers 50 line.

be apparent from the following description of the drawing.

Fig. l shows the subscribers substation pro- 55' vided with ra hand operated switch and the two lower winding of the induction coil IC.

These and other features of the invention will line conductors extending to the main exchange. Fig. 2 shows the apparatus at the main office. Referring now to Fig. l, the substation circuit shown is substantially the same as that shown and described in Patent No. 1,657,635, issued Jany5 uary 31, 1928, to T. G. Martin. Associated with this substation circuit is a switch having a hand operated knurled knob I2 for rotating wiper i3 over the talk segment I4, grounded segment I5,

first listening position segment I6, and other T0 listening segments I'I and IB. The wiper I3 is electrically connected to the lower line conductor Il and the listening segments I'I and I8 are con-v nected by way of varying resistances R and RI as shown. When wiper I3 is stopped on segment 15" Il the resistance R is connected in shunt of the In a similar manner wiper I3 and segment I8 connect, the resistance RI in shunt of the lower winding of induction coil IC. Additional shunt circuits could' 20 be added for reducing the volume, if desired.

In Fig. 2 theV subscribers line conductors I9 and II terminate in an individual amplifying unit comprising a standard well-known amplifying arrangement, ,switching control relays 2B, 30, 40 50, and BI), and two choke coils. The line conyductors I0 and II extend through both windings of the dilferential relay and normally over back contacts of the cut-in relay 3l) to the line switch indicated by the rectangle. The line switch has accessV to first selector switches which: in turn have access to connector switches or second selectors dependent upon the capacity of the auto matic system. The line switches, selector. and connectorsrare of the well-known type used in 5 automatic telephone systems. Only the battery feed relays and the busying arrangement of the connector switches are diagrammatically shown. In order to describe the invention it will be assumed that the subscriber removes rthe receiver to initiate a call. In response to theremoval of the receiver the line relay in the line switch is operated over the subscribers loop in the usual manner; the battery and ground connections being furnished from the line switch. The subscribers loop in this case includes conductors 'it and 1I, back contacts and armatures 32 and 33.' and the upper and lower windings of differential relay 2D. Relay 2i! does not operate over this 50 circuit because both windings oppose each other. 'In response to the operation of the line switch line relay, ground is connected the usual manner to lead 'I2 rto busy the line and to light the filament of the amplifier tube, and the lineswitch is operated inthe well-known manner to select an idle rst selector switch.

The subscriber now operates the calling device in accordance with the digits of the called subscriber to operate the selector and connector switches to complete the connection to the called lineI in the well-known manner. When the called party answers the talking circuit is completed over the heavy talking conductors through back contacts and armatures 32 and 33 and the windings of diierential relay 2li; talking battery being furnished through the windings of the line relay in the connector. The called party talking battery is furnished through the windings of the back bridge relay in the connector. The preceding operationsA are old and well-known and have been briey described to illustrate the circuits when the amplifier is not in use. Y

Assuming now that the subscriber at the sub- Y station is hard of hearing and desires to cut in the amplifier. The subscriber turns the knurled knob I2 and wiper I3 in the direction of the arrow to segment I6 on the rst listening position.

When wiper I3 engages the elongated grounded segment I5, the diiereritial relay 2B is energized because the lower winding is shunted from ground at the substation, segment I5, wiper I3, conductor I I, lower winding of relay 29, armature 33 and back contact, conductor 'II, through the switches to ground through the lower winding oi the battery feed relay. At armature ZI relay 29 completes the circuit for energizing relay 6U as follows: from grounded conductor 12, armature 2i, armature 5I and back contact, armature 4I, and through the winding of relay 6) to battery. Relay @Il energizes and at armature 6I connects grounded conductor 'I2 to cut-in relay 30 to cause the latter relay to energize. At'armature 52 relay 60 prepares the circuit for relay 5D but this relay cannot energize because it is short-circuited.

When wiper I3 passes oi of grounded segment I5 differential relay 2D is again balanced and therefore deenergizes. At armature ZI relay 2D opens the short circuit around relay 5B whereupon relay 50 now energizes in series with relay 60. Relay 50 is energized and relay- 6,0 is maintained energized over the following circuit: from grounded conductor 72, armatures 43 and` 52 and through the windings oi relays 54.! and lilll in series to battery. At armature 5I relay 50 opens the original circuit of relay 50 at its back contacts and at its front contacts prepares the circuit for release relay 40.

Cut-in relay 3B, upon energizing, cuts in the amplifier by connecting the conductors 'I0 and II to the input circuit at armature 3|, by'disconnecting conductors 'IB and 'II from armatures 32 and 33, and by connecting the out-put circuit of the amplifier to the subscribers line conductors Ill and II by way of the front contactsof armatures 32 and 33. Speech current transmitter over conductors 'I0 and II is now amplified and transmitted over conductors I!) and II to the substation receiver. The choke coils are provided to prevent the A. C. speech currentsfrom being transmitted back over conductors 'IU and 'II while at the same time provide circuits Vover which the differential relay 20 may be controlled.

In case the volume is too loud or the transmitter and receiver howl, the subscriber by further rotating wiper I3 can place a resistance R or Ril in shunt of the lower winding rof the induction coil IC. Since these resistances vary, the volume can be reduced as desired by this shunting arrangement.

Since the amplier provides only one Way amplification, the subscriber` at the substation, in order to talk, must return the hand operated switch I2 and wiper I3 to its normal or talk position I4. In response to restoring wiper I3 to talk position I4, wiper I3 again encounters grounded segment I5 for a sufficient time to allow the unbalancing and operation of differential relay 20. Ground at the substation through segment I5,

wiper I3 and conductor I I, extends through the lower winding of relay 20, the lower choke coil and over conductor 'IIJ to ground through the lower windings of the battery feed relay for shunting the lower winding of relay 20. The upper winding of relay 29 is energized from ground over the substation loop to conductor Ill, upper winding of relay 20, upper choke coil, conductor 10, to battery through the upper Winding of the battery feed relay. Relay 20, upori operating, at armature 2l completes the circuit for energizing release relay 4B as follows: fromY grounded conductor 'I2 armature V2I,'armature 5I and front Contact, and winding of release relay 40 to battery. At armature 42 relay 4U completes a locking circuit for itself and at armature 43 opens the circuit of relays 50 and 60, which deenergize. At armature 6I relay SI! opens the circuit of Cutin relay 38 which deenergizes to disconnect the At armature 5I relay 5I] prepares the circuit Vto relay 69. When wiper I3 leaves segment I5 the diierential relay releases armature 2l to release relay 40 thereby restoring the circuits to normal. the heavy conductors in the usual manner. From the foregoing it will be seen that the amplifier may be cut-in and cut-out of the circuit whenever desired by theoperation of the switching device at the substation.

In case Vthe substation in Fig. 1 is calledl the amplifier may be operated in the same manner as 1. In a telephone system, a main exchange, a

calling subscribers substation, a subscribers line connecting the substation to said exchange,- means at said exchange controlled from said calling subscribers substation for extending said line to another subscribers line, an amplifier at the main exchange, and means at the substation controlled at will by said calling subscriber for momentarily grounding one of the line conductors of said line to bring the amplifier into circuit at any time to amplify the incoming Voice currents tol said line.

2. In a telephone system, a main exchange, a subscriberfs substation, a subscribers lineV ccnnecting the substation to said exchange, anamplier at the main exchange, means at the substation controlled at will by a callingsubscriber for momentarily grounding one of the line conductors of said line to' bring the amplifier into circuit at any time to amplify the incoming voice currents to said line, and means including said last means operated responsive to a second nioinentary grounding of said line conductor for cutting said amplier out of circuit with said line. 3. AIn a telephone system, a main exchange, a

The subscriber now talks over subscribers line connected to said exchange, means at the exchange controlled by the subscriber on said line for establishing a connection with a wanted subscriber including a talking circuit arranged for non-amplified transmission, a holding circuit including said talking circuit for maintaining said established telephone connection, an amplifier at the exchange, means for switching from said normal talking circuit to an amplified talking circuit including said amplifier for amplifying incoming voice currents to said line, choke coils included in said holding circuit to maintain the connection and for preventing the amplified voice currents from being transmitted back in the reverse direction in response to the operation of said means, and subscriber controlled means for at will operating said switching means over the subscribers line to connect said amplified talking circuit or said normal talking circuit to said established connection.

4. In a telephone system, a main exchange, a subscribers line connected to said exchange, an amplifier at the exchange normally disconnected from in circuit with said line, means controlled by the subscriber on said line for establishing a connection including a normal two-way talking circuit for transmitting incoming and outgoing voice currents over said line, means for switching from said normal talking circuit to an amplier talking circuit including said amplifier to amplify incoming voice currents to said line, means for preventing the amplified incoming voice currents from being transmitted back over the incoming path, and subscriber controlled means for controlling said switching means over said subscribers line at will to disconnect the normal talking circuit from said connection and to connect said amplifier to said connection while said connection is established.

5. In a telephone system, a main exchange, a calling subscribers line connected in a talking connection through said exchange with a wanted subscriber, an amplifier at the main exchange, switching means at the exchange, a relay at the exchange, means at said calling subscribe-rs station actuated at will by the calling subscriber for operating said relay once for each actuation of said means to control the operation of said switching means, said switching means operatively connecting the amplifier in circuit with said connection to amplify the voice currents incoming to said line in response to the rst actuation of said station means and relay and disconnecting the amplifier from in circuit with said connection in response to the second actuation of said station means and relay while the said connection is maintained.

6. In a telephone system, a main exchange, a calling subscribers line connected in a talking connection through said exchange with a wanted subscriber, an amplifier at the main exchange,

, switching means at the exchange, a relay at the exchange, means at said calling subscribers station actuated at will by the calling subscriber for operating said relay once for each actuation of said means to control the operation. of said switching means, said switching means operatively connecting the amplifier in circuit with said connection to amplify the voice currents incoming tol said line in response to the first actuation of said station means and relay and disconnecting the amplifier from in circuit with said connection in response to the second actuation of said station means and relay, and means whereby said station means is effective for operating said relay while said connection is maintained.

7. In a. telephone system, a main exchange, a subscribers line terminating in said exchange, an amplifier at the main exchange, a connecting relay for said amplier, a normal non-amplified two-way talking circuit including back contacts on said connecting relay and said line; an amphfied talking circuit including said line, said amplifier, and front contacts on said connecting relay for amplifying incoming voice currents to said line; and means individual to said line operated at the will of the subscriber thereon for operating said connecting relay to complete either talking circuit after a connection is established between said line and a called subscribers line.

8. In a telephone system., a main exchange, a subscribers line terminating in said exchange, an amplifier at the main exchange, a connecting relay for said amplifier, anormal non-amplified two-way talking circuit including back contacts on said connecting relay and said line; an amplied talking circuit including said line, said amplifier, and front contacts o-n said connecting relay for amplifying incoming voice currents to l said line; means individual to said line operated at the will of the subscriber thereon for operating said connectingk relay to complete either talking circuit after a connection is established between the subscriber on said line and a wanted subscriber, and choke coils connected in shunt of said back contacts on said connecting relay for preventing the amplified incoming voice currents from feeding back over the talking circuit.

9. In atelephone system, a. main exchange, a calling subscribers substation, a line connecting the substation to said exchange, an amplier at the main exchange, means at the substation controlled at will by the calling subscriber for momentarily grounding one of the line conductors of said line, a differential relay normally connected in series with both line conductors of said line and operated in response to the grounding of one line conductor, and means controlled by the operation of said differential relay for bringing said amplifier into circuit to amplify the incoming voice currents to said line.

10. In an automatic telephone system, an exchange, a calling subscribers line terminating in said exchange, means at said exchange controlled by said calling subscriber for completing a normal talking connection between said calling subscriber and a desired called subscriber, an amplifier included in said means normally disconnected from said normal talking connection; a switch operated at will by said calling subscriber for controlling the connecting of said amplifier in series with said normal talking connection to amplify the voice currents received by the calling subscriber, for varying the volume of the voice currents received by the' calling subscriber, and for disconnecting the amplifier from the normal talking connection; said switch controlling operations only effective during the time said connection is established. Y

CLARENCE E. LOMAX. 

